A New York City police officer's illegal chokehold killed Eric Garner last month, and his death has been ruled a homicide, the medical examiner announced Friday.

Officer Daniel Pantaleo and another officer tried to arrest the 6-foot-3, 350-pound father of six for selling untaxed cigarettes on a Staten Island street July 17. Video shot by a passerby showed Pantaleo, an eight-year NYPD veteran, grabbing the 43-year-old Garner around the neck as he and his partner wrestled him to the ground.

Medical examiner spokeswoman Julie Bolcer said Garner died from "the compression of his chest and prone positioning during physical restraint by police." Asthma and heart disease contributed to his death, she said.

The Staten Island district attorney is investigating, and Attorney General Eric Holder said the Justice Department is "closely monitoring" the probe.

Pantaleo was stripped of his badge and gun and given desk duty. His partner, who has not been identified, was reassigned but allowed to keep his gun and badge.

"We all have a responsibility to work together to heal the wounds from decades of mistrust and create a culture where the police department and the communities they protect respect each other-and that's a responsibility that Commissioner Bratton and I take very seriously," Mayor Bill de Blasio said in a statement.

Gwen Carr, mother of Eric Garner, left, and his sister Ellisha Garner hug during a rally at the National Action Network headquarters July 26 in New York.(Photo: John Minchillo, AP)